I-MooFest(POJ 1990)

#include <cstdio>
#include <iostream>
#include <sstream>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>
using namespace std;
#define ll long long
#define _cle(m, a) memset(m, a, sizeof(m))
#define repu(i, a, b) for(int i = a; i < b; i++)
#define MAXN  20005

struct P{
   ll v, p;
   bool operator < (const P& t) const {
     return t.v > v;
   }
}cow[MAXN];
ll c_ount[MAXN] = {0};
ll total[MAXN] = {0};
ll sum_tot[MAXN] = {0};
int n;

ll lowbit(ll x)
{
    return x & (-x);
}

void add(int x, int d, ll c[])
{
    while(x < MAXN) {
        c[x] += d;
        x += lowbit(x);
    }
}

ll Sum(ll x, ll c[])
{
    ll ret = 0;
    while(x > 0)
    {
        ret += c[x];
        x -= lowbit(x);
    }
    return ret;
}

int main()
{
    scanf("%d", &n);
    repu(i, 1, n + 1) scanf("%lld%lld", &cow[i].v, &cow[i].p);
    sort(cow + 1, cow + n + 1);
    repu(i, 1, n + 1) sum_tot[i] = sum_tot[i - 1] + cow[i].p;
    ll sum = 0, num_cow = 0, sum_total = 0;
    add(cow[1].p, 1, c_ount);
    add(cow[1].p, cow[1].p, total);
    repu(i, 2, n + 1) {
      num_cow = Sum(cow[i].p, c_ount);
      sum_total = Sum(cow[i].p, total);
      sum += cow[i].v * (num_cow * cow[i].p - sum_total
          + (sum_tot[i - 1] - sum_total - (i - 1 - num_cow) * cow[i].p));
      add(cow[i].p, 1, c_ount);
      add(cow[i].p, cow[i].p, total);
    }
    printf("%lld\n", sum);
    return 0;
}